PENSION AND OTHER POSTRETIREMENT BENEFITS - NET PERIODIC BENEFIT COST (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Net periodic benefit cost [Abstract]
Service Cost	$ 5,583	$ 6,442	$ 4,989
Interest Cost	17,294	13,778	11,772
Expected Return on Plan Assets	(20,195)	(18,672)	(14,105)
Amortizations:
Prior Service Credits	105	116	131
Actuarial Loss	9,550	11,528	10,282
Net Periodic Benefit (Credit) Cost	12,337	13,192	13,069
Curtailment and Special Termination Costs	955	7,324	0
Capitalized Benefit Costs	(2,008)	(2,243)	(4,723)
Affiliate SERP Allocations	0	0
Deferred Benefit Costs	(2,411)	(1,987)	(527)
Total Net Periodic Benefit (Income) Expense	8,873	16,286	7,819
Other Postretirement Benefits
Net periodic benefit cost [Abstract]
Service Cost	533	945	910
Interest Cost	2,884	2,430	2,418
Expected Return on Plan Assets	(4,571)	(4,286)	(3,411)
Amortizations:
Prior Service Credits	(561)	(344)	(344)
Actuarial Loss	1,163	903	1,238
Net Periodic Benefit (Credit) Cost	(552)	(352)	811
Curtailment and Special Termination Costs	0	1,286	(106)
Capitalized Benefit Costs	(201)	(290)	(46)
Affiliate SERP Allocations	(59)	(265)
Deferred Benefit Costs	357	580	0
Total Net Periodic Benefit (Income) Expense	(396)	1,224	659
South Jersey Gas Company | Pension Benefits
Net periodic benefit cost [Abstract]
Service Cost	3,621	5,073	4,303
Interest Cost	11,067	10,010	9,925
Expected Return on Plan Assets	(11,028)	(12,513)	(11,366)
Amortizations:
Prior Service Credits	95	112	127
Actuarial Loss	8,224	10,074	8,692
Net Periodic Benefit (Credit) Cost	11,979	12,756	11,681
Capitalized Benefit Costs	(1,437)	(1,943)	(4,723)
Affiliate SERP Allocations	0	0
Deferred Benefit Costs	(2,411)	(1,987)	(527)
Total Net Periodic Benefit (Income) Expense	4,590	4,965	4,196
South Jersey Gas Company | Supplemental Employee Retirement Plan
Amortizations:
Affiliate SERP Allocations	(3,541)	(3,861)	(2,235)
South Jersey Gas Company | Other Postretirement Benefits
Net periodic benefit cost [Abstract]
Service Cost	343	583	582
Interest Cost	1,863	1,698	1,897
Expected Return on Plan Assets	(3,220)	(3,449)	(3,101)
Amortizations:
Prior Service Credits	(474)	(257)	(257)
Actuarial Loss	1,042	695	972
Net Periodic Benefit (Credit) Cost	(446)	(730)	93
Capitalized Benefit Costs	(155)	(257)	(46)
Affiliate SERP Allocations	(6)	(143)
Deferred Benefit Costs	357	580	0
Total Net Periodic Benefit (Income) Expense	$ (244)	$ (407)	$ 47